Half-metallic Ferromagnetic Heusler Alloys Research Articles

Effect on Annealing Temperature (Ta) of Ternary Full Fe2CrSi Heusler Alloy Nanoparticles for Spin-Based Device Applications

The ternary full Heusler alloy nanoparticle Fe2CrSi compounds were prepared using mechanical alloy method. The as-prepared sample was observed as amorphous in nature and further increases various annealing temperatures (like 700 °C, 800 °C, and 900 °C) in nitrogen gas atmosphere for 5 h in tubular furnace using quartz tube. X-ray diffraction studies confirmed the formation of Cu2MnAl-type structure instead of the conventional L21 disordered structure. Through Williamson-Hall plot (W-H plot), the uniform deformation model was used to get low value of strain-induced broadening. In the surface morphology, elemental composition studies were carried out using HRSEM with EDS. The presence of Fe2CrSi with the particle size of ~ 35 nm was also observed using high-resolution scanning electron microscopy and elemental composition study confirmed the presence of Fe, Cr, and Si. The magnetic properties of Fe2CrSi nanoparticles were studied showing ferromagnetic behavior and low coercivity of soft magnetic nature. Half metallic ferromagnetic Heusler alloys have wide range of applications from medical imaging to data storage for its profound performance on spintronics.

Investigation of phase transition in electronic structure and magnetic properties of Fe2-x Co x TiSn Heusler alloys

ABSTRACT The structural, electronic, mechanical and magnetic properties of Fe2-x Co x TiSn (x = 0, 0.5, 1, 1.5, 2) Heusler alloys in L21 (Cu2MnAl prototype) and XA (Hg2CuTi) phases are analysed. The structural optimization confirms the stability of these alloys in L21 phase. As the pressure is increased, the structural phase transition from L21 to XA phase is predicted at the pressures of 123.34, 74.27, 47.22, 43.18 and 31.25 GPa in Fe2TiSn, Fe1.5Co0.5TiSn, Fe1.0Co1.0TiSn, Fe0.5Co1.5TiSn and Co2TiSn, respectively. Fe2TiSn is identified as a non-magnetic semiconductor using electronic structure calculation. The effect of substitution of Co for Fe on electronic structure and magnetic property of Fe2TiSn is investigated. It is found that Co substituted Fe1.5Co0.5TiSn, Fe1.0Co1.0TiSn and Fe0.5Co1.5TiSn are found to be half-metallic ferromagnetic Heusler alloys. The elastic constants are calculated to ensure mechanical stability. This study opens a way out for the potential application of these alloys as spintronic materials.

Soft Ferromagnetic Properties of Half-Metallic Mn2CoAl Heusler Alloy Nanoparticles for Spintronics Applications

The ternary full Heusler alloy Mn2CoAl nanoparticles were synthesized by using co-precipitation technique. The as-prepared sample was observed for amorphous nature and further increased at various annealing temperatures (like 700 °C, 800 °C and 900 °C) in argon gas atmosphere for 5 h. X-ray diffraction studies were performed, and the pattern confirms the formation of Hg2CuTi-type structure of the XA or Xα disorder structure. Williamson-Hall plot (W-H plot) was used to find the uniform deformation model so as to get low value of strain-induced broadening. The presence of Mn2CoAl with the particle size ≈ 50 nm was obtained from high-resolution scanning electron microscopy (HR-SEM), and the elemental analysis study confirms the presence of Mn, Co, and Al. UV-Visible absorption spectrum shows the wide absorption peak at 470 nm and the estimated band gap energy value at Eg = 0.8 eV (from Tauc plot) for 900 °C annealed sample. Synthesized Mn2CoAl nanoparticles induced ferromagnetic behavior due to composition deviation and as a result displayed low coercivity of soft magnetic behavior. Half-metallic ferromagnetic Heusler alloys have a wide range of applications from medical imaging to data storage, and also it has profound spintronics applications.

Experimental observation of anomalies in the electrical, magnetic, and galvanomagnetic properties of cobalt-based Heusler alloys with varying transition elements

The residual resistivity, Hall effect, and magnetization of Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were considered at T = 4.2 K and in fields up to 100 kOe. It is shown that as the number of valence electrons z ranges from 26 to 32, significant changes in the residual resistivity ρ0, magnetization Ms, sign and magnitude of the normal R0 and anomalous RS Hall effect coefficients are observed during the transition from Co2TiSi to Co2NiSi. It is established that there is a clear correlation between the values ρ0, R0, RS and Ms, depending on the number z, which can be associated with the appearance of a half-metal ferromagnetic state and/or spin gapless semiconductor. As z changes, the anomalous Hall effect coefficient has a power-law dependence on the residual electrical resistivity with an exponent of k = 3.1, which diverges with existing theories but agrees well with the experimental data obtained earlier for similar half-metallic ferromagnetic Heusler alloys.

ChemInform Abstract: Equiatomic Quaternary Heusler Alloys: A Material Perspective for Spintronic Applications

AbstractReview: 110 refs.

Equiatomic quaternary Heusler alloys: A material perspective for spintronic applications

Half-metallic ferromagnetic (HMF) materials show high spin polarization and are therefore interesting to researchers due to their possible applications in spintronic devices. In these materials, while one spin sub band has a finite density of states at the Fermi level, the other sub band has a gap. Because of their high Curie temperature and tunable electronic structure, HMF Heusler alloys have a special importance among the HMF materials. Full Heusler alloys with the stoichiometric composition X2YZ (where X and Y are the transition metals and Z is a sp element) have the cubic structure with four interpenetrating fcc sublattices. When each of these four fcc sublattices is occupied by different atoms, a quaternary Heusler structure with different structural symmetry is obtained. Recently, these equiatomic quaternary Heusler alloys (EQHAs) with 1:1:1:1 stoichiometry have attracted a lot of attention due to their superior magnetic and transport properties.

Specific features of the electrical resistivity of half-metallic ferromagnets Co2 MeAl (Me = Ti, V, Cr, Mn, Fe)

The transport properties of half-metallic ferromagnetic Heusler alloys Co2 MeAl (Me = Ti, V, Cr, Mn, Fe are transition 3d metals) have been measured in the temperature range of 4–900 K. The specific features of the behavior of the resistivity have been considered in the framework of the two-current model of conductivity that takes into account the existence of the energy gap in the electronic spectra of the alloys near the Fermi level of one of electron subbands that differs in the spin direction.

Peculiarities of the electronic transport in Co2CrAl and Co2CrGa half-metallic ferromagnets

We present results on the transport properties of the half-metallic ferromagnetic Heusler alloys Co2CrAl and Co2CrGa in the temperature range from 4 to 900 K. The peculiarities of the resistivity and the absolute differential thermoelectric power are considered within a two-current model of conductivity, taking into account the energy gap at the Fermi level in the electronic spectrum of alloys for electrons with spin opposite to the direction of the magnetization vector.

Specific features of the properties of half-metallic ferromagnetic Heusler alloys Fe2MnAl, Fe2MnSi, and Co2MnAl

The structural, magnetic, and electrical properties of half-metallic Heusler alloys Fe2MnAl, Fe2MnSi, and Co2MnAl have been investigated in the temperature range of 4–900 K. According to the X-ray diffraction analysis, these alloys have the B2 and L21 structures with different degrees of atomic order. The magnetic state of the alloys is considered as a two-sublattice ferrimagnet. The electrical resistivity and thermoelectric power have been discussed in the framework of the two-current conduction model taking into account the existence of an energy gap in the electronic spectrum of the alloys near the Fermi level for the subband with spin-down (minority) electrons.

Electronic transport in Co-based half-metallic ferromagnetic Heusler alloys

The electroresistivity of the Co-based half-metallic ferromagnetic Co2CrGa, Co2CrAl, Co2VAl, Co2MnAl Heusler alloys and the Ni2MnGa ferromagnets were measured in the temperature range from 4.2 to 900 K. Specific features in the electrical resistivity of the half-metallic ferromagnetic Heusler alloys were observed, which can be explained in terms of the two-current conduction model, taking into account the existence of an energy gap in the electron spectrum near the Fermi level.

Specific features of the electrical resistivity of half-metallic ferromagnets Fe2MeAl (Me = Ti, V, Cr, Mn, Fe, Ni)

The transport properties of half-metallic ferromagnetic Heusler alloys Fe2MeAl (where Me = Ti, V, Cr, Mn, Fe, and Ni are 3d transition elements) have been measured in the temperature range of 4–900 K. The specific features in the behavior of the electrical resistivity have been considered in terms of the two-current conduction model, which takes into account the presence of an energy gap in the electron spectrum of the alloys near the Fermi level.

Specific features of the electrical resistance of half-metallic ferromagnetic alloys Co2CrAl and Co2CrGa

It has been shown by comparing the results of studying the electrical and magnetic properties of the halfmetallic ferromagnetic Heusler alloys Co 2CrAl and Co2CrGa with the calculations of their elec� tronic structure that high values of the electrical resistivity ρ are caused by a disordered distribution of atoms over the sites of the L21 cubic structure, and the anomalous behavior of ρ(T) is associated with the transfor� mation of the electronic spectrum due to the ferromagnetictoparamagnetic transition.

FMR study of thin films of Co2Cr0.6Fe0.4Al and Co2MnSi Heusler alloys

The method of ferromagnetic resonance (FMR) was used to study magnetic properties of thin films of half-metallic ferromagnetic Heusler alloys Co2Cr0.6Fe0.4Al and Co2MnSi depending on the film thickness and the presence or absence of a vanadium buffer layer. It is shown that the FMR method is a highly efficient technique for studying nanoscale magnetic properties of thin films, especially for the investigation of their magnetic inhomogeneities and anisotropy. Samples of Co2Cr0.6Fe0.4Al and Co2MnSi were prepared by magnetron-sputtering deposition on substrates of single-crystal silicon dioxide (SiO2) with an orientation (100). It has been shown that the magnetic properties of thin Co2Cr0.6Fe0.4Al films strongly depend on both the film thickness (25 or 100 nm) and the presence of an intermediate vanadium layer (50 nm). Well-resolved spin-wave modes were observed in the sample 100 nm thick without a vanadium buffer layer, which made it possible to determine the parameter of spin stiffness D for this ferromagnet. Two series of thin films of Co2MnSi have also been studied, which were prepared on a buffer layer of vanadium (42 nm thick): (1) with various thicknesses (4–100 nm) and a fixed annealing temperature (450°C) and (2) with a fixed thickness (80 nm) and various annealing temperatures (425–550°C). It has been shown that in the series of Co2MnSi films with a variable thickness (4–100 nm) the greatest value of magnetization is reached for a film with a thickness of 61 nm. The investigations of the other series of films, which were annealed at various temperatures, show that to achieve both a greater magnetization and a better structural homogeneity, annealing at temperatures T ≥ 450°C is required. In addition, low-intensity spin-waves were observed in some samples with thicknesses of 100 and 61 nm, which made it possible to estimate the spin-stiffness parameter D for the Co2MnSi Heusler alloy as well.

Spin Density in Real and Momentum Space in Multi-Atom Alloys by KKR-CPA Method

The application of the spin-polarized version of multiple scattering the- ory for obtaining electron charge and spin densities in both real and momen- tum spaces of concentrated, multi-atom disordered alloys is presented. This method is based on the Korringa—Kohn—Rostoker (KKR) band structure ap- proach and coherent potential approximation (CPA) method. The effective one-electron potential is constructed within local spin density approxima- tion. The magnetic neutron form factors are in real space of our main inter- est. With the recent developments of new synchrotron photon sources, the Compton profile becomes the most interesting target in momentum space. In the most of examples, spin momentum density and its specific structure due � to Fermi surface will be shown. To get accurate enough description in mo- mentum space and quantity like Compton profile, the determination of the Fermi surface must be done with high precision. In this context we show how to apply generalized Lloyd formula for accurate determination of the Fermi level. Also we show how to use efficiently complex energy integration method for the computation of matrix elements, G(τ, τ) or G(p, p), of the KKR—CPA Green . function. Results for the iron—silicon ferromagnetic binary alloys and half-metallic ferromagnetic Heusler alloys are presented. PACS numbers: 71.15.Cr, 71.18.+y, 78.90.+t